The present invention generally relates to electrochemical cells, i.e., batteries, and more particularly to a low profile closure assembly for closing and sealing the open end of a battery container.
Conventional alkaline electrochemical cells generally include a steel cylindrical can having a positive electrode, referred to as the cathode, which comprises manganese dioxide as the active material. The electrochemical cell also includes a negative electrode referred to as the anode, which comprises zinc powder as the active material. In a bobbin-type cell construction, the cathode is typically formed against the interior surface of the steel can, while the anode is generally centrally disposed in the can. Alternately, in jelly-roll cells, the anode and cathode are spirally wound. A separator is located between the anode and the cathode, and an alkaline electrolyte solution simultaneously contacts the anode, the cathode, and the separator. A conductive current collector is commonly inserted into the anode active material, and a seal assembly, which includes a seal member, provides closure to the open end of the steel can to seal the active electrochemical materials in the sealed volume of the can.
Cylindrical alkaline cells are commonly closed by inserting a preassembled collector and seal assembly in the open end of the steel can. The collector and seal assembly typically includes the collector nail, an annular nylon seal, and an inner metal cover for radially supporting the nylon seal. The can typically has a taper or an inwardly extending bead at its open end which serves to support the collector and seal assembly in the desired orientation prior to securing it in place. After the collector and seal assembly has been inserted, an outer metal cover is placed over the assembly and the assembly and cover are secured in place by radially squeezing the can against the collector and seal assembly and outer cover and crimping the edge of the can over the peripheral lip of the collector and seal assembly and outer cover to secure the outer cover and collector and seal assembly within the open end of the can. The conventional rollback outer cover has a peripheral edge that is folded back, which results in a non-uniform compression of the seal. Additionally, electrochemical cells commonly employ electrochemically active materials, such as zinc, which generate hydrogen gas during storage and sometimes during or following service use. When the battery can is closed, excessive build-up of high pressure gases within the sealed can may cause damage to the cell and/or the device in which cell is employed.
In order to handle the potentially excessive build-up of pressure in the electrochemical cell, conventional batteries have employed voluminous seals which provide pressure release venting. One pressure relief approach has employed a resealable valve system that periodically releases excessive gas pressure from within the active volume. Another approach employs the use of a vent formed in the annular nylon seal which is intended to rupture upon experiencing excessive pressure build-up in the cell. According to yet another approach, the cell employs a circular thinned region formed in the annular nylon seal. However, the amount of space occupied by the conventional seal, the inner metal cover, and the outer metal cover, can be significant.
The greater the space occupied by the collector and seal assembly, the less space that there is available within the cell for the electrochemically active materials. Consequently, a reduction in the amount of electrochemically active materials that may be provided within the cell results in shorter service life for the cell. It is therefore desirable to maximize the internal volume within an electrochemical cell that is available for the electrochemically active components.